The present invention is an enhancement to structures used for sediment removal from a fluid stream by separation, such as the devices taught in taught in U.S. Pat. Nos. 5,746,911; 6,264,835 and 7,875,174. These type separators typically have three separate flow paths for influent water, and treat contaminated water by separation of floating materials and non-buoyant materials from the water, at varying levels of efficiency depending on the influent flow rate.
When it rains on a parking lot, a road, or other impervious surface, the water will not permeate into the ground as it once did, and instead this water will runoff and discharge directly into a stream or receiving body. Since these impervious surfaces typically have vehicles or traffic on them, an accumulation of pollutants will occur between rain events. This runoff is then concentrated because it is unable to be absorbed into the ground, and the pollutants are concentrated as well. This has caused a severe degradation of our watersheds. Most of the pollutants are typically washed off in the beginning (which is usually the less intense part of the storm), consequently the first runoff water is the most critical to treat. In an effort to minimize the impacts of this, systems have been developed to treat this water by removing the pollutants by separation or filtration.
Because precipitation occurs at variable rates from a small trickle to a monsoon, the system must be able to capture the pollutants and not release them during the high flow events. Consequently treating stormwater creates additional difficulties because the system must be able to clean the water yet be able to pass very intense storms or flooding could occur. Separators are able to remove floating material and materials that sink in water by skimming and settling methods.
In addition, significant amounts of semi-buoyant or neutral buoyant material is also entrained within the fluid flow. Separators in such systems remove particles of different densities than water quite well, however, they can have difficulty in removing neutrally buoyant debris. This neutral buoyancy material can then pass through the system and be discharged, producing a less than optimal treatment of the run off water.